1. Field of the Invention
This invention relates to a process for the manufacture of molded, high resiliency (HR), polyurethane foams. More particularly, this invention relates to a process for producing molded high resiliency, polyurethane foams without using volatile organic blowing agents such as chlorofluorocarbons, methylene chloride, halocarbons or other volatile organic compounds such as pentane.
2. Description of the Prior Art
High resilience foam technology has provided improved physical foam properties and processing advantages compared with the conventional technology of foam production. The HR foams generally possess outstanding resiliency and cushioning qualities.
In the manufacture of HR molded foam, it is frequently desired to produce articles of different firmness on the same production line. This is currently done by feeding an inert third stream containing volatile organic compounds as "blowing agents", such as chlorofluorocarbons, to a foam mixing device. The use of these blowing agents lowers the foam stiffness as well as the density of the manufactured article. Adequate stiffness is a requirement for end use application. Additionally, foams prepared in this manner can have undesirable properties because the density is too low.
In recent years, processes have been sought by the polyurethane industry for making molded, high resiliency polyurethane foam products while eliminating, or at least substantially reducing, the amount of inert volatile organic blowing agents, particularly chlorofluorocarbons (CFCs). CFCs are known to damage the earth's protective ozone layer, an effect which is expected to lead to a greater incidence of skin cancer and related maladies caused by solar exposure, as well as possible catastrophic climate changes. The U.S. Environmental Protection Agency recently has pushed for a complete phaseout of the use of such ozone-depleting chemicals. Another blowing agent, methylene chloride, also has fallen into disfavor due to concern about short and possibly longer term health effects. Thus, the current trend is to avoid or minimize the use of such inert blowing agents, if possible, in the preparation of polyurethane foams.
Surprisingly, it has been discovered that the use of an inert blowing agent stream in the making of molded, high resiliency polyurethane foams as taught in the prior art can be replaced by a "reactive" third feed stream that controls the stiffness of the foam without adversely affecting other foam properties such as density and density-dependent properties. By "reactive" is meant that the components of the third stream of the present invention react chemically with at least one other component of the other streams, i.e., components of the third stream are not inert.